As a material constituting a toner to be used for forming an image, an ester wax having excellent fixability, particularly excellent high-temperature offset resistance, and a crystalline polyester resin having excellent low-temperature offset resistance are known. In recent years, in order to comply with energy efficiency standards in each country, which become stricter, the low-temperature fixation of a toner is demanded for reducing environmental burden.
For example, when an ester wax which has a small carbon number and shows a sharp intensity ratio distribution such that the ratio of the proportion of a carbon number showing the maximum intensity ratio to the proportion of the other carbon numbers is small is used, the low-temperature offset resistance is improved as compared with the case where a natural wax such as rice wax or carnauba wax is used. However, the storage property of the toner is deteriorated. On the other hand, when an ester wax which has a large carbon number and shows a sharp intensity ratio distribution of carbon numbers is used, since the straight chain of the ester wax is long, the low-temperature offset resistance is not excellent. By using this ester wax in combination with a crystalline polyester resin having excellent low-temperature offset resistance, the Tg of the toner is significantly lowered, so that the low-temperature offset can be improved.
In a toner using an ester wax which has a large carbon number and shows a sharp intensity ratio distribution of carbon numbers and a crystalline polyester in combination, a wax is deposited (bled out) on a toner surface when the toner is left under a high temperature and high humidity environment. Due to this, a carrier surface in a developer is contaminated with a wax component to deteriorate the chargeability during the service life, and therefore, toner scattering or fogging on an image is deteriorated so that it becomes hard to prolong the service life. By making the intensity ratio distribution of carbon numbers in the ester wax broader, and also by controlling the proportion of the ester wax having a small carbon number, the deposition of the wax when the toner is left under a high temperature environment can be suppressed.
However, even if a toner using an ester wax improved in this manner and a crystalline polyester in combination is mounted on a high-speed machine, the low-temperature fixation and the prolongation of the service life are further more demanded. If the proportion of components having a small carbon number in the ester wax is increased, the low-temperature fixation can be further achieved, however, the storage stability, which is an inconsistent object, is deteriorated. Moreover, the fluidity of the toner is deteriorated, resulting in the deterioration of toner scattering, and therefore, this method cannot achieve the prolongation of the service life. In this manner, it is very hard to achieve all of the low-temperature fixation in a high-speed machine, the storage stability, and the prolongation of the service life.
An object of the embodiments herein is to provide a toner having low-temperature fixability and storage stability, and capable of prolonging the service life.
According to an embodiment, a toner including: toner particles containing a coloring agent, an amorphous polyester, a crystalline polyester having an endothermic peak temperature of T2 as measured by a differential scanning calorimeter, and an ester wax having an endothermic peak temperature of T1 as measured by a differential scanning calorimeter (provided that T1<T2); and inorganic oxide particles externally added to the toner particles is provided. The ester wax contains multiple ester compounds, each having a carbon number selected from 32 to 54 and obtained by reacting an alkyl carboxylic acid component with an alkyl alcohol component, and when the ion intensity ratio of each ester compound having a different carbon number is expressed as percentage, the content (a) of the ester compound having a carbon number of (On) showing the maximum intensity ratio is from 20 to 55% by weight of the entire ester wax, and the content of the ester compounds having a carbon number of 38 or less is 10% by weight or less, of the entire ester wax. The sum (g) of the content (e) of the ester compound having a carbon number of (Cn+2) and the content (f) of the ester compound having a carbon number of (Cn+4) satisfies the following formula: 0.065≦g/a≦0.200. The inorganic oxide particles contain hydrophobic silica having an average primary particle diameter of 8 to 35 nm.